This invention relates to endless belts of the cog type containing a shear, abrasion and noise resistant inner cover element which is substantially free of the body elastomer at its surface, and further relates to a method for producing such belts. This invention relates to and defines an improvement over my related U.S. Pat. No. 3,772,929 and assigned to the assignee of the subject invention and hereby incorporated by reference.
It has been recognized that power transmission belts constructed of a castable elastomer, e.g., liquid polyurethane, offer a number of significant advantages over conventional rubber belting. Among these advantages are that the liquid cast belt is less susceptible to flex fatigue, it can be driven around smaller sheaves, and demonstrates improved load life. These cast belts may be vacuum spin cast in a single operation as contrasted to the numerous steps required to build conventional rubber toothtype belts. However, many of the castable timing belts, and particularly those constructed of urethane, are often noiser and run hotter than a comparable rubber belt due primarily to the difference in coefficient of friction of the material. The urethane belt is generally more aggressive as it enters and leaves the sprocket or sheave and builds up considerable heat at the interfaces. This heat build-up reduces the efficiency of the belt and the higher operating temperatures can reduce belt life considerably by lowering the tear strength of the cog, or by attacking the bond between the elastomer body and tensile cord embedded therein.
One solution to the noise and heat-build-up problem is to reduce the coefficient of friction of the sheave-engaging surface of the belt by isolating or removing as much of the cast elastomer from near the surfaces of the belt which come into contact with the sprocket teeth or flanges. This approach was taken in my above-mentioned U.S. Pat. No. 3,772,929 in which I was able to isolate a large portion of the elastomer from the sheave-engaging surfaces of the belt by incorporating a wearresistant fabric layer along the surface of the belt together with the incorporation of cross cords in the body of the cogs, thus eliminating much of the elastomer in the critical areas. However, as acknowledged in my U.S. Pat. No. 3,772,929, there was still present an outer skim coating of elastomer on the surface of the belt. This outer layer, even though relatively thin, e.g., about 2 mils in thickness, exhibits high abrasion and wearresistance and by virtue of its high coefficient of friction causes significant increases in heating and noise level of the belt, particularly for heavy duty applications.
It is a primary object of the invention to provide a belt construction and method therefor which overcome drawbacks of prior constructions and in which the castable elastomer is isolated from the outer surface of the wear-resistant fabric layer positioned along the sheave-engaging surface of the belt.